A solid electrolytic capacitor using an electrically conducting polymer has a basic structure such that an oxide dielectric film is formed on the surface of a valve-acting metal such as aluminum, tantalum or titanium, previously subjected to etching treatment, an electrically conducting polymer which works out to solid electrolyte is formed on the oxide dielectric film, an anode lead is connected to the anode terminal (the metal surface area where the solid electrolyte is not formed) and a cathode lead is connected to the electrically conducting layer containing the electrically conducting polymer. The solid electrolytic capacitor is manufactured by finally sealing the device as a whole with insulating resins such as epoxy resins.
Such solid electrolytes using an electrically conducting polymer for the solid electrolyte can be reduced in the equivalent series resistance and the leakage current as compared with solid electrolytic capacitors using manganese dioxide or the like for the solid electrolyte. This is advantageous in manufacturing a capacitor capable of coping with the tendency of electronic equipment toward higher performance and smaller size. Accordingly, a large number of production methods have been proposed therefor.
In order to produce a high-performance solid electrolytic capacitor using an electrically conducting polymer, it is indispensable to secure electrical insulation of the anode part which works out to an anode terminal, from the cathode part comprising an electrically conducting layer containing an electrically conducting polymer.
As the masking means for insulating the anode part from the cathode part of a solid electrolytic capacitor, for example, a method of coating, printing or potting epoxy resins, phenol resins or the like on an unformed area and curing the resin to prevent passing of electricity (see, JP-A-3-95910 (the term “JP-A” as used herein means an “unexamined published Japanese patent applications”)), a method of electrodepositing a solution containing a polyamic salt on at least a part of the valve-acting metal in the area where the solid electrolyte is not formed, thereby forming a polyamic acid film, and dehydration-curing the film by heating to form a polyimide film (see, JP-A-5-47611), a method of forming a tape or resin coating film part made of polypropylene, polyester, silicon or fluorine-based resin so as to prevent the solid electrolyte from climbing up (see, JP-A-5-166681), and a method of forming an insulating resin layer on the surface of a metal substrate in the boundary part between the area which works out to an anode terminal and the area where the capacitor is formed, and removing the insulating resin layer in the area other than the capacitor part to expose the metal substrate (see, JP-A-9-36003).
The method of using phenol resins or epoxy resins as the masking material (JP-A-3-95910) is disadvantageous in that the capacitor is greatly damaged when pressed by-external force, because the elastic modulus of resin is high and the stress against strains is high.
The method of forming a polyimide film by electro-deposition (JP-A-5-47611) may successfully form a film even inside the pore parts as compared with ordinary coating methods, however, the production cost increases because of necessity of the electrodeposition step and moreover, a dehydration step at a high temperature is necessary so as to form the polyimide film.
The method of forming an insulating resin-made tape or resin coating film part so as to prevent the solid electrolyte from climbing up at the manufacturing (JP-A-5-166681) has difficulty in firmly fixing the tape (film) at edge parts of the substrate and bears a risk of polymer solid electrolyte as the solid electrolyte invading the anode side.
The method of forming an insulating resin layer and then removing the insulating resin layer in the area other than the capacitor part to expose the metal substrate (JP-A-9-36003) includes a substantially useless step of once forming an insulating resin layer and then removing it.
As described above, the conventional masking means are insufficient and actually it has not been clear yet what is like the form (structure) of a masking that can insulate without fail the anode part from the cathode part of a solid electrolytic capacitor.